The present invention relates to an injection molding soft resin composition and uses thereof. More particularly, the invention relates to an injection molding soft resin composition which is a polyolefin composition containing an ethylene/xcex1-olefin copolymer and is capable of producing injection molded articles with high productivity, said injection molded articles being excellent in softness, low gloss and hand and being favorably used as soft toys, daily use miscellaneous articles, etc., and the invention also relates to an injection molded article of the composition and a painted article of the injection molded article.
Polyolefins, such as a relatively soft ethylene/xcex1-olefin copolymer having a Shore A hardness of 40 to 95, particularly an ethylene/xcex1-olefin copolymer having a Shore A hardness of 40 to 70, are low-crystalline or non-crystalline, and therefore, if they are used alone in the injection molding, the following molding disadvantages are liable to occur.
That is, a period of time necessary for a molten resin charged in a desired mold by injection to reach hardened state enough for withdrawal of a molded article from the mold (said time being referred to as xe2x80x9ccooling timexe2x80x9d hereinafter) is long; and molding defects such as sink mark and flash occur. A long cooling time means along molding cycle, and this causes lowering of productivity of injection molded articles. Occurrence of molding defects such as sink mark and flash means a high rate of occurrence of defective injection molded articles, and such defects should not be present in the molded articles. Particularly, a low-crystalline soft ethylene/xcex1-olefin copolymer has a low hardening rate, and hence the above-mentioned molding disadvantages are liable to take place.
For the purpose of increasing the hardening rate only, a filler such as an inorganic filler or a resin having a relatively high hardening rate such as high-crystalline polypropylene or polyethylene has only to be added to the low-crystalline or non-crystalline ethylene/xcex1-olefin copolymer. This method, however, has a disadvantage that the softness inherent in the ethylene/xcex1-olefin copolymer is impaired, though the hardening rate of the ethylene/xcex1-olefin copolymer is increased.
A crosslinked olefin thermoplastic elastomer composition comprising an xcex1-olefin copolymer and a polypropylene resin is excellent in softness, heat resistance and low gloss and has a higher hardening rate compared with the ethylene/xcex1-olefin copolymer, when used alone, so that the composition is widely used as a soft polyolefin resin capable of being subjected to injection molding. This composition, however, has low tensile strength, and when the composition is molded into a tubular molded product, the product is easily broken.
Further, any paint or primer showing good adhesion to the ethylene/xcex1-olefin copolymer does not exist, and a molded article produced from the ethylene/xcex1-olefin copolymer is not suitable for uses where painting is indispensable.
Accordingly, there is desired development of an injection molding soft resin composition, from which injection molded articles excellent in low gloss, mechanical properties such as tensile strength and appearance can be produced with high productivity without impairing softness inherent in the low-crystalline or non-crystalline ethylene/xcex1-olefin copolymer, an injection molded article thereof, and further an injection molded article having excellent adhesion of coating.
The present invention is intended to solve such problems associated with the prior art as described above, and it is an object of the invention to provide an injection molding soft resin composition, from which injection molded articles excellent in low gloss, mechanical properties such as tensile strength and appearance can be produced with high productivity without impairing softness inherent in the low-crystalline or non-crystalline ethylene/xcex1-olefin copolymer, and an injection molded article of the composition, e.g., an injection molded article employable as a soft toy or a daily use miscellaneous article.
It is another object of the invention to provide an injection molded article having been subjected to color finish with a paint and showing excellent adhesion of coating.
The injection molding soft resin composition according to the invention is a composition comprising:
(A) an ethylene/xcex1-olefin copolymer in an amount of 99 to 5 parts by weight, said copolymer comprising ethylene and an xcex1-olefin of 3 to 10 carbon atoms, and
(B) a thermoplastic elastomer composition in an amount of 1 to 95 parts by weight, said thermoplastic elastomer composition being obtained by dynamically heat treating a crystalline polyolefin resin (a) and an olefin copolymer rubber (b) in the presence of a crosslinking agent,
the total of said components (A) and (B) being 100 parts by weight,
wherein the ethylene/xcex1-olefin copolymer (A) has:
(i) a Shore A hardness (JIS K 6253) of 40 to 95,
(ii) a melt flow rate MFR2.16 (ASTM D 1238, 190xc2x0 C., load of 2.16 kg) of 1.0 to 100 g/10 min, and
(iii) a density (ASTM D 1505) of 855 to 900 kg/m3, and the thermoplastic elastomer composition (B) has:
(i) a gel content of 30 to 100%, and
(ii) a Shore A hardness (JIS K 6253) of 40 to 95.
The injection molding soft resin composition of the invention desirably has a Shore A hardness (JIS K 6253) of 40 to 95 and a melt flow rate MFR2.16 (ASTM D 1238, 190xc2x0 C., load of 2.16 kg) of 1.0 to 100 g/10 min.
The ethylene/xcex1-olefin copolymer (A) desirably has:
(iv) a molecular weight distribution (Mw/Mn), as determined by gel permeation chromatography (GPC), of 1 to 3, and
(v) a ratio (MFR10/MFR2.16) of a melt flow rate MFR10 (ASTM D 1238, 190xc2x0 C., load of 10 kg, g/10 min) to the MFR2.16 (g/10 min) ranging from 5 to 20.
The ethylene/xcex1-olefin copolymer (A) may be a mixture of two or more kinds of the ethylene/xcex1-olefin copolymers (A).
The injection molded article according to the invention comprises the above-mentioned injection molding soft resin composition.
The injection molded article of the invention may have been subjected to painting on the surface.
The painted article of an injection molded article according to the invention is preferably an injection molded article having been subjected to color finish with a paint, said color finish being made by coating the surface of the above-mentioned injection molded article with a primer comprising a styrene elastomer resin having been graft polymerized with a monomer having an xcex1,xcex2-monoethylenically unsaturated group and then conducting the painting.
The painted article of an injection molded article according to the invention is particularly preferably an injection molded article having been subjected to color finish with a paint, said color finish being made by coating the surface of the above-mentioned injection molded article with a mixture of the primer and a photo polymerization initiator, subjecting the coated surface to UV treatment and then conducting the painting.
Each of the toy and the daily use miscellaneous article according to the invention comprises the above-mentioned injection molded article.